Documents detailing the upcoming BIS 4.0 have been found and there are some decent improvements on the way for those non-corporate BES users. Some of the new features include:
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Integration with BlackBerry ID (BBID)

Improved BIS End User Communications

Automatic Login improvements

Support for new service tiers

Google Calendar Improvements

In BIS 4.0, we’ll also be seeing more from the BIS emails including notifications to upgrade the OS. Overall, it doesn’t look like there is anything to go nuts about, but it’s a decent upgrade. At some point, we’re going to start seeing a lot more cloud-based services including contact management, calendar and memopad, all stored with access based on your BlackBerry ID.